The present invention relates to automotive vehicle hydraulic braking systems and more particularly to a mechanism for controlling the application of hydraulic fluid pressure thereby preventing wheel lock at braking.
Means for preventing wheel lock in automotive vehicles and for securing vehicle stability at braking have included anti-skid devices hitherto proposed which employ atmospheric pressure and a negative pressure in order to effect operation of a valve and to electrically control wheel cylinder hydraulic pressure upon the occurrence of wheel lock. In such devices, the decrease of pressure upon the vehicle brake pedal and the shortening of the braking distance can be effected with high precision by utilizing the coefficient of friction which occurs between the vehicle tires and the road surface. However, the controls involved are rather complicated and the number of components which must be utilized is large. It is thus found that prior art devices can be disadvantageous due to the fact that they are expensive and are prone to malfunction.
In order to eliminate such disadvantages, the present invention proposes that in combination with a hydraulic brake circuit there be provided a hydraulic brake pressure control device which holds the wheel cylinder hydraulic pressure at a certain value during wheel lock with a relief valve or pressure regulator being also provided to control the wheel cylinder hydraulic pressure after wheel lock has been released.